I have an Ultegra 9sp setup that I am very happy with (just replaced the sSTI hifters after 15k miles) and after reading all of the threads on this site would like to switch to a R-700 compact crank. There are a lot of comments that the R-700 works fine with either 6500 or 6600 front Ds, but no one says anything about chains. Am I correct that it will work with a 9sp chain along with 6600 front D? One would think that the chain might be almost more important then the derailleur when it comes to shifting. Thanks.

I have an R-700 in a Frankendrive: 9 speed Tiagra STIs, DA 7800 RD, currently no FD, HG-93 (Ultegra 9-speed) chain, 105 9-speed cassette. For me, when on the 34-t chain-ring, while on the smaller cogs (cross-gearing), the chain rubs on th 50-t chain-ring. Not really an issue for me since I just don't use the combination, but I believe this is along the lines of your concern. Haven't installed a FD yet since currently that bike is my trainer/rain bike.

I have an Ultegra 9sp setup that I am very happy with (just replaced the sSTI hifters after 15k miles) and after reading all of the threads on this site would like to switch to a R-700 compact crank. There are a lot of comments that the R-700 works fine with either 6500 or 6600 front Ds, but no one says anything about chains. Am I correct that it will work with a 9sp chain along with 6600 front D? One would think that the chain might be almost more important then the derailleur when it comes to shifting. Thanks.
I recently installed the Shimano compact crank on my otherwise Dura Ace 9-speed equipped bike, it works perfectly.